122 GERM-CELL CYCLE IN ANIMALS 



fifteen nurse cells lacking this nuclear substance. 

 Thus as Paulcke's theory demands, the difference 

 between the nurse cells and the oocytes is the result 

 of internal and not external causes. 



Giardina considered the formation of the chromatic 

 ring as a sort of synapsis, and later (1902) distin- 

 guished between a complete synapsis, such as 

 ordinarily occurs in the germ-cell cycle, and a partial 

 synapsis as exhibited by Dytiscus. Regarding the 

 significance of this differential mitosis, he maintains 

 that this phenomenon is the cause of the differen- 

 tiation into nurse cells and oocytes, resulting in a 

 complete amount of chromatin in the keimbahn 

 cells and perhaps also an unequal distribution of cyto- 

 plasmic substances. As in the case of Ascaris and 

 Miastor, it might better be regarded as a means of 

 depriving the nurse cells of part of their chromatin. 

 Moreover, Boveri (1904) has compared the chroma- 

 tin-diminution in Ascaris with Giardina's differ- 

 ential mitoses. Debaisieux (1909) and Giinthert 

 (1910) have confirmed Giardina's results, and the 

 latter studied two other DYTISCID^E, Acilius and 

 Colymbetes, which also exhibit differential mitoses 

 similar except in certain details. Giinthert found 

 that the chromatic ring is composed of fine granules 

 which may split off from the surface of the chromo- 

 somes (compare with Ascaris and Miastor) and stain 

 like cytoplasm. He interprets this as " Zerfallspro- 

 dukte" of the chromosomes. Debaisieux, on the 

 other hand, claims that this cast-out nuclear material 

 is nucleolar rather than chromatic in nature. 



